Silicon carbide (SiC) has been widely used as industrial materials including polishing or abrasive materials, ceramics sintered materials, and conductive materials. In recent years, awareness about energy conservation and utilization of natural renewable energy while abandoning nuclear power generation among people has been higher than before. Because of such social background, there is a demand for a high-purity silicon carbide powder which can be used as monocrystalline materials for power semiconductors.
As a technique of mass-producing silicon carbide in an industrial scale, there has been known a method of using a siliceous raw material containing silicon (Si) (for example, silica sand) and a carbonaceous raw material containing carbon (for example, petroleum coke) as raw materials and heating the materials at 1,600° C. or more by using an Acheson furnace, thereby producing silicon carbide by means of a direct reduction reaction.
A high-purity silicon carbide powder cannot be obtained by the conventional production methods using an Acheson furnace, because impurities are contained at a high content in raw materials and it is difficult to control the impurities.
Therefore, there have been proposed various methods of upgrading the purity of a low-purity silicon carbide powder. For example, Patent Literature 1 discloses a method of producing a high-purity silicon carbide powder, the method including providing a silicon carbide powder containing impurities at high contents in a vacuum vessel and heating the powder at a vacuum degree of 9×10−5 to 1×10−2 torr and a temperature of 1,500 to 1,700° C., thereby removing the impurities contained in the silicon carbide powder.
However, the method disclosed in Patent Literature 1 which has a step of heating in vacuum requires complex devices and high-cost, and does not allow for mass production at one time in an industrial scale.
Patent Literature 2 discloses a method of producing a high-purity silicon carbide powder, the method including introducing a mixture of a silicon carbide powder containing impurities at high contents and hydrofluoric acid into a sealed container and heating the mixture under increased pressure.
However, there are problems in that hydrofluoric acid is difficult to handle because it is harmful to humans and hazardous, and in that the method disclosed in Patent Literature 2 does not allow for mass processing of the silicon carbide powder in an industrial scale.